<<I have noted that some provision for versioning of the normalization
algorithms is presaged in UTR#15. It makes me shudder, thinking what will
happen what my (fictitious) typesetting program, 2000 Unicode XPress
Version 3, would do when presented with post-Unicode-3.0 data which has the
æ-grave precomposed as well as æ with combining grave. Easy to tell:
sorting and searching won't work for the precomposed latter but it will
work for the decomposed sequence; that is, my Unicode XPress will be broken
until such time as its owners spend time and money on revving up to the new
normalization algorithm, and until such time as I spend my money on an
upgrade I didn't need except for some vowels I never use.

In other words, it's not enough that we have to upgrade fonts for new
versions of the standard (which is reasonable as scripts get added) but all
our apps as well.>>

Yes if the normalisation data is hard coded into your applications - but
they
could be designed to read in a file containing table information for
new or additional normalisation and sorting rules. Perhaps what is needed
is a standard format for such files.